Superactive multimetallic catalytic composite

ABSTRACT

A novel superactive multimetallic hydrocarbon conversion catalytic composite comprises a combination of a catalytically effective amount of a pyrolyzed rhenium carbonyl component with a porous carrier material containing a uniform dispersion of a catalytically effective amount of a platinum group component which is maintained in the elemental metallic state. In a highly preferred embodiment, this novel catalytic composite also contains a catalytically effective amount of a halogen component. The platinum group component, pyrolyzed rhenium carbonyl component and optional halogen component are preferably present in the multimetallic catalytic composite in amounts, calculated on an elemental basis, corresponding to about 0.01 to about 2 wt. % platinum group metal, about 0.01 to about 5 wt. % rhenium and about 0.1 to about 3.5 wt. % halogen. A key feature associated with the preparation of the subject catalytic composite is reaction of a rhenium carbonyl complex with a porous carrier material containing a uniform dispersion of a platinum group metal maintained in the elemental state, whereby the interaction of the rhenium moiety with the platinum group moiety is maximized due to the platinophilic (i.e. platinum-seeking) propensities of the carbon monoxide ligand used in the rhenium reagent.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of my prior copending application Ser.No. 833,332 filed Sept. 14, 1977. All of the teachings of this priorapplication are incorporated herein by reference.

The subject of the present invention is a novel superactivemultimetallic catalytic composite which has remarkably superioractivity, selectivity and resistance to deactivation when employed in ahydrocarbon conversion process that requires a catalytic agent havingboth a hydrogenation-dehydrogenation function and a carboniumion-forming function. The present invention, more precisely, involves anovel dual-function superactive multimetallic catalytic composite whichquite surprisingly enables substantial improvements in hydrocarbonconversion processes that have traditionally used a platinum groupmetal-containing, dual function catalyst. According to another aspect,the present invention comprehends the improved processes that areproduced by the use of the instant superactive platinum-rhenium catalystsystem which is characterized by a unique reaction between a rheniumcarbonyl compound and a porous carrier material containing a uniformdispersion of a platinum group component maintained in the elementalmetallic state, whereby the interaction between the rhenium moiety andthe platinum group moiety is maximized on an atomic level. In a specificaspect, the present invention concerns a catalytic reforming processwhich utilizes the subject catalyst to markedly improve activity,selectivity and stability characteristics associated therewith to adegree not heretofore realized for a platinum-rhenium catalyst system.Specific advantages associated with use of the present superactiveplatinum-rhenium system in a catalytic reforming process relative tothose observed with the prior art platinum-rhenium catalyst system, are:(1) Substantially increased ability to make octane at low severityoperating conditions; (2) Increased capability to maximize C₅ +reformate and hydrogen production by operating at severity levels atwhich the prior art system has not been successfully employed; (3)Ability to substantially expand the catalyst life before regenerationbecomes necessary in conventional temperature-limited catalyticreforming units; (4) Vastly increased tolerance to conditions which areknown to increase the rate of production of deactivating coke deposits;(5) Significantly diminished requirements for amount of catalyst toachieve same results as the prior art catalyst system at no sacrifice incatalyst life before regeneration; and (6) Capability of operating atsignificantly increased charge rates with the same amount of catalystand at similar conditions as the prior art catalyst system without anysacrifice in catalyst life before regeneration.

Composites having a hydrogenation-dehydrogenation function and acarbonium ion-forming function are widely used today as catalysts inmany industries, such as the petroleum and petrochemical industry, toaccelerate a wide spectrum of hydrocarbon conversion reactions.Generally, the carbonium ion-forming function is thought to beassociated with an acid-acting material of the porous, adsorptive,refractory oxide type which is typically utilized as the support orcarrier for a heavy metal component such as the metals or compounds ofmetals of Groups V though VIII of the Periodic Table to which aregenerally attributed the hydrogenation-dehydrogenation function.

These catalytic composites are used to accelerate a wide variety ofhydrocarbon conversion reactions such as hydrocracking, hydrogenolysis,isomerization, dehydrogenation, hydrogenation, desulfurization,cyclization, polymerization, alkylation, cracking, hydroisomerization,dealkylation, transalkylation, etc. In many cases, the commercialapplications of these catalysts are in process where more than one ofthe reactions are proceeding simultaneously. An example of this type ofprocess is reforming wherein a hydrocarbon feedstream containingparaffins and naphthenes is subjected to conditions which promotedehydrogenation of naphthenes to aromatics, dehydrocyclization ofparaffins to aromatics, isomerization of paraffins and naphthenes,hydrocracking and hydrogenolysis of naphthenes and paraffins, and thelike reactions, to produce an octane-rich or aromatic-rich productstream. Another example is a hydrocracking process wherein catalysts ofthis type are utilized to effect selective hydrogenation and cracking ofhigh molecular weight unsaturated materials, selective hydrocracking ofhigh molecular weight materials, and other like reactions, to produce agenerally lower boiling, more valuable output stream. Yet anotherexample is a hydroisomerization process wherein a hydrocarbon fractionwhich is relatively rich in straight-chain paraffin compounds iscontacted with a dual-function catalyst to produce an output stream richin isoparaffin compounds.

Regardless of the reaction involved or the particular process involved,it is of critical importance that the dual-function catalyst exhibit notonly the capability to initially perform its specified functions, butalso that it has the capability to perform them satisfactorily forprolonged periods of time. The analytical terms used in the art tomeasure how well a particular catalyst performs its intended functionsin a particular hydrocarbon reaction environment are activity,selectivity, and stability. And for purposes of discussion here, theseterms are conveniently defined for a given charge stock as follows: (1)activity is a measure of the catalyst's ability to convert hydrocarbonreactants into products at a specified severity level where severitylevel means the conditions used--that is, the temperature, pressure,contact time, and presence of diluents such as H₂ ; (2) selectivityrefers to the amount of desired product or products obtained relative tothe amount of reactants charged or converted; (3) stability refers tothe rate of change with time of the activity and selectivityparameters--obviously, the smaller rate implying the more stablecatalyst. In a reforming process, for example, activity commonly refersto the amount of conversion that takes place for a given charge stock ata specified severity level and is typically measured by octane number ofthe C₅ + product stream; selectivity refers to the amount of C₅ + yield,relative to the amount of the charge, that is obtained at the particularactivity or severity level; and stability is typically equated to therate of change with time of activity, as measured by octane number ofC₅ + product and of selectivity as measured by C₅ + yield. Actually thelast statement is not strictly correct because generally a continuousreforming process is run to produce a constant octane C₅ + product withseverity level being continuously adjusted to attain this result; andfurthermore, the severity level is for this process usually varied byadjusting the conversion temperature in the reaction so that, in pointof fact, the rate of change of activity finds response in the rate ofchange of conversion temperatures and changes in this last parameter arecustomarily taken as indicative of activity stability.

As is well known to those skilled in the art, the principal cause ofobserved deactivation or instability of a dual-function catalyst when itis used in a hydrocarbon conversion reaction is associated with the factthat coke forms on the surface of the catalyst during the course of thereaction. More specifically, in these hydrocarbon conversion processesthe conditions utilized typically result in the formation of heavy, highmolecular weight, black, solid or semi-solid, carbonaceous materialwhich is a hydrogen-deficient polymeric substance having properties akinto both polynuclear aromatics and graphite. This material coats thesurface of the catalyst and thus reduces its activity by shielding itsactive sites from the reactants. In other words, the performance of thisdual-function catalyst is sensitive to the presence of carbonaceousdeposits or coke on the surfact of the catalyst. Accordingly, the majorproblem facing workers in this area of the art is the development ofmore active and/or selective catalytic composites that are not assensitive to the presence of these carbonaceous materials and/or havethe capability to suppress the rate of the formation of thesecarbonaceous materials on the catalyst. Viewed in terms of performanceparameters, the problem is to develop a dual-function catalyst havingsuperior activity, selectivity, and stability characteristics. Inparticular, for a reforming process the problem is typically expressedin terms of shifting and stabilizing the C₅ + yield-octane relationshipat the lowest possible severity level--C₅ + yield being representativeof selectivity and octane being proportional to activity.

I have now found a dual-function superactive multimetallic catalyticcomposite which possesses improved activity, selectivity and stabilitycharacteristics relative to similar catalysts of the prior art when itis employed in a process for the conversion of hydrocarbons of the typewhich have heretofore utilized dual-function, platinum groupmetal-containing catalytic composites such as processes forisomerization, hydroisomerization, dehydrogenation, desulfurization,denitrogenization, hydrogenation, alkylation, dealkylation,disproportionation, polymerization, hydrodealkylation, transalkylation,cyclization, dehydrocyclization, cracking, hydrocracking, halogenation,reforming and the like processes. In particular, I have now establishedthat a superactive multimetallic catalytic composite, comprising acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous carrier material containing acatalytically effective amount of a platinum group component, can enablethe performance of hydrocarbon conversion processes utilizingdual-function catalysts to be substantially improved if the platinumgroup component is relatively uniformly dispersed throughout the porouscarrier material prior to contact with the rhenium carbonyl reagent, ifthe oxidation state of the platinum group metal is maintained in theelemental metallic state prior to and during contact with the rheniumcarbonyl reagent and if high temperature treatment in the presence ofoxygen and/or water of the resulting reaction product is avoided. Aspecific example of my discovery involves my finding that a superactiveacidic multimetallic catalytic composite, comprising a combination of acatalytically effective amount of a pyrolyzed rhenium carbonyl componentwith a porous carrier material containing a uniform dispersion of acatalytically effective amount of a platinum group component maintainedin the elemental metallic state and a catalytically effective amount ofa halogen component, can be utilized to substantially improve theperformance of a hydrocarbon reforming process which operates on a lowoctane gasoline fraction to produce a high octane reformate oraromatic-rich reformate. In the case of a reforming process, some of themajor advantages associated with the use of the novel multimetalliccatalytic composite of the present invention include: (1) theacquisition of the capability to operate in a stable manner in a highseverity operation; for example, a low or moderate pressure reformingprocess designed to produce a C₅ + reformate having an octane of atleast about 100 F-1 clear; (2) substantially increased activity foroctane upgrading reactions relative to the performance of prior artbimetallic platinum-rhenium catalyst systems as exemplified by theteachings of Kluksdahl in his U.S. Pat. No. 3,415,737; (3) increasedcapability to operate for extended periods of time in high severity,temperature-limited existing catalytic reforming units. In sum, thepresent invention involves the remarkable finding that the addition of apyrolyzed rhenium carbonyl component to a porous carrier materialcontaining a uniform dispersion of a catalytically effective amount of aplatinum group component maintained in the elemental metallic state, canenable the performance characteristics of the resulting superactivemultimetallic catalytic composite to be sharply and materially improvedrelative to those associated with the prior art platinum-rheniumcatalyst system.

It is, accordingly, an object of the present invention to provide asuperactive multimetallic hydrocarbon conversion catalyst having vastlysuperior performance characteristics relative to the prior artplatinum-rhenium catalyst system when utilized in a hydrocarbonconversion process. A second object is to provide a superactivemultimetallic acidic catalyst having dual-function hydrocarbonconversion performance characteristics which are relatively insensitiveto the deposition of coke-forming, hydrocarbonaceous materials thereonand to the presence of sulfur contaminants in the reaction environment.A third object is to provide preferred methods of preparation of thissuperactive multimetallic catalytic composite which methods insure theachievement and maintenance of its unique properties. Another object isto provide a substantially improved platinum-rhenium catalyst systemhaving superior activity, selectivity and stability characteristicsrelative to the platinum-rhenium catalyst system of the prior art.Another object is to provide a novel acidic multimetallic hydrocarbonconversion catalyst which utilizes a pyrolyzed rhenium carbonylcomponent to beneficially interact with and selectively promote anacidic catalyst containing a halogen component and a uniform dispersionof a platinum group component maintained in the metallic state.

Without the intention of being limited by the following explanation, Ibelieve my discovery that rhenium carbonyl can, quite unexpectedly, beused under the circumstances described herein to synthesize an entirelynew type of platinum-rhenium catalyst system, is attributable to one ormore unusual and unique routes to greater platinum-rhenium interactionthat are opened or made available by the novel chemistry associated withthe reaction of a rhenium carbonyl reactant with a supported, uniformlydispersed platinum metal. Before considering in detail each of thesepossible routes to greater platinum-rhenium interaction it is importantto understand that: (1) "Platinum" is used herein to mean any one of theplatinum group metals; (2) The unexpected results achieved with mycatalyst system are measured relative to the conventionalplatinum-rhenium catalyst system as taught in for example the KluksdahlU.S. Pat. No. 3,415,737; (3) The expression "rhenium moiety" is intendedto mean the catalytically active form of the rhenium entity in thecatalyst system; and (4) Metallic carbonyls have been suggestedgenerally in the prior art for use in making catalysts such as in U.S.Pat. Nos. 3,591,649, 4,048,110 and 2,798,051, but no one to my knowledgehas ever suggested using these reagents in the platinum-rhenium catalystsystem, particularly where substantially all of the platinum componentof the catalyst is present in a reduced form (i.e. the metal) prior toincorporation of the rhenium carbonyl component. One route to greaterplatinum-rhenium interaction enabled by the present invention comes fromthe theory that the effect of rhenium on a platinum catalyst is verysensitive to the particle size of the rhenium moiety; since in myprocedure the rhenium is put on the catalyst in a form where it iscomplexed with a carbon monoxide molecule which is known to have astrong affinity for platinum, it is reasonable to assume that when theplatinum is widely dispersed on the support, one effect of the CO ligandis to pull the rhenium moiety towards the platinum sites on thecatalyst, thereby achieving a dispersion and particle size of therhenium moiety in the catalyst which closely imitates the correspondingplatinum conditions (i.e. this might be called a piggy-back theory). Thesecond route to greater platinum-rhenium interaction is similar to thefirst and depends on the theory that the effect of rhenium on a platinumcatalyst is at a maximum when the rhenium moiety is attached toindividual platinum sites; the use of platinophilic CO ligands, ascalled for by the present invention, then acts to facilitate adsorptionor chemisorption of the rhenium moiety on the platinum site so that asubstantial portion of the rhenium moiety is deposited or fixed on ornear the platinum site where the platinum acts to anchor the rhenium,thereby making it more resistant to sintering at high temperature. Thethird route to greater platinum-rhenium interaction is based on thetheory that the active state for the rhenium moiety in therhenium-platinum catalyst system is the elemental metallic state andthat the best platinum-rhenium interaction is achieved when theproportion of the rhenium in the metallic state is maximized; using arhenium carbonyl compound to introduce the rhenium into the catalyticcomposite conveniently ensures availability of more rhenium metalbecause all of the rhenium in this reagent is present in the elementalmetallic state. Another route to greater platinum-rhenium interaction isderived from the theory that oxygen at high temperature is detrimentalto both the active form of the rhenium moiety (i.e. the metal) and thedispersion of same on the support (i.e. oxygen at high temperatures issuspected of causing sintering of the rhenium moiety); since thecatalyst of the present invention is not subject to high temperaturetreatment with oxygen after rhenium is incorporated, maximumplatinum-rhenium interaction is obviously preserved. The final theoryfor explaining the greater platinum-rhenium interaction associated withthe instant catalyst is derived from the idea that the active sites forthe platinum-rhenium catalyst are basically platinum metal crystallitesthat have had their surface enriched in rhenium metal; since the conceptof the present invention requires the rhenium to be laid down on thesurface of well-dispersed platinum crystallites via a platinophilicrhenium carbonyl complex, the probability of surface enrichment isgreatly increased for the present procedure relative to that associatedwith the random, independent dispersion of both crystallites that hascharacterized the prior art preparation procedures. It is of course tobe recognized that all of these factors may be involved to some degreein the overall explanation of the impressive results associated with mysuperactive catalyst system. A further fact to be kept in mind is thatthe conventional platinum-rhenium catalyst system has never been notedfor an activity improvement (i.e. the consensus of the art is that itgives the same activity as the all platinum catalyst system it haslargely supplanted) but its strong suit has always been very impressivestability; in contrast, my superactive platinum-rhenium catalyst systemas demonstrated in the attached examples and in FIGS. 1-3,conservatively speaking, gives about twice as much activity as theconventional platinum-rhenium catalyst system and, even more surprising,this activity advantage is accomplished at no sacrifice in the superiorstability property which is characteristic of the old platinum-rheniumcatalyst system.

Against this background then, the present invention is in oneembodiment, a novel bimetallic catalytic composite comprising acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous material containing a uniformdispersion of a catalytically effective amount of a platinum groupcomponent maintained in the elemental metallic state.

In another embodiment, the subject catalytic composite comprises acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous carrier material containing acatalytically effective amount of a halogen component and a uniformdispersion of a catalytically effective amount of a platinum groupcomponent maintained in the elemental metallic state.

In yet another embodiment the present invention involves a combinationof a pyrolyzed rhenium carbonyl component with a porous carrier materialcontaining a halogen component and a uniform dispersion of a platinumgroup component maintained in the elemental metallic state, wherein thecomponents are present in amounts sufficient to result in the compositecontaining, calculated on an elemental basis, about 0.01 to about 2 wt.% platinum group metal, about 0.01 to about 5 wt. % rhenium and about0.1 to about 3.5 wt. % halogen.

In still another embodiment, the present invention comprises any of thecatalytic composites defined in the previous embodiments wherein theporous carrier material contains, prior to the addition of the pyrolyzedrhenium carbonyl component, a catalytically effective amount of acomponent selected from the group consisting of tin, lead, germanium,cobalt, nickel, iron, tungsten, chromium, molybdenum, bismuth, indium,gallium, cadmium, zinc, uranium, copper, silver, gold, one or more ofthe rare earth metals and mixtures thereof.

In another aspect, the invention is defined as a catalytic compositecomprising the pyrolyzed reaction product formed by reacting acatalytically effective amount of a rhenium carbonyl compound or complexwith a porous carrier material containing a uniform dispersion of acatalytically effective amount of a platinum group metal maintained inthe elemental metallic state, and thereafter subjecting the resultingreaction product to pyrolysis conditions selected to decompose therhenium carbonyl component.

A concomitant embodiment of the present invention involves a method ofpreparing any of the catalytic composites defined in the previousembodiments, the method comprising the steps of: (a) reacting a rheniumcarbonyl compound with a porous carrier material containing a uniformdispersion of a platinum group component maintained in the elementalmetallic state, and thereafter, (b) subjecting the resulting reactionproduct to pyrolysis conditions selected to decompose the rheniumcarbonyl component, without oxidizing either the platinum group orrhenium components.

A further embodiment involves a process for the conversion of ahydrocarbon which comprises contacting the hydrocarbon and hydrogen withthe superactive catalytic composite defined in any of the previousembodiments at hydrocarbon conversion conditions.

A highly preferred embodiment comprehends a process for reforming agasoline fraction which comprises contacting the gasoline fraction andhydrogen with the superactive multimetallic catalytic composites definedin any one of the prior embodiments at reforming conditions selected toproduce a high octane reformate.

An especially preferred embodiment is a process for the production ofaromatic hydrocarbons which comprises contacting a hydrocarbon fractionrich in aromatic precursors and hydrogen with an acidic catalyticcomposite comprising a combination of a catalytically effective amountof a pyrolyzed rhenium carbonyl component with a porous carrier materialcontaining a catalytically effective amount of a halogen component and auniform dispersion of a catalytically effective amount of a platinumgroup component maintained in the elemental metallic state, saidcontacting being performed at aromatic production conditions selected toproduce an effluent stream rich in aromatic hydrocarbons.

Other objects and embodiments of the present invention relate toadditional details regarding the essential and preferred catalyticingredients, preferred amounts of ingredients, appropriate methods ofcatalyst preparation, operating conditions for use with the novelcatalyst in the various hydrocarbon conversion processes in which it hasutility, and the like particulars, which are hereinafter given in thefollowing detailed discussion of each of the essential and preferredfeatures of the present invention.

Considering first the porous carrier material utilized in the presentinvention, it is preferred that the material be a porous, adsorptive,high surface area support having a surface area of about 25 to about 500m² /g. The porous carrier material should be relatively refractory tothe conditions utilized in the hydrocarbon conversion process, and it isintended to include within the scope of the present invention carriermaterials which have traditionally been utilized in dual-functionhydrocarbon conversion catalysts such as: (1) activated carbon, coke, orcharcoal; (2) silica or silica gel, silicon carbide, clays, andsilicates including those synthetically prepared and naturallyoccurring, which may or may not be acid treated for example, attapulgusclay, china clay, diatomaceous earth, fuller's earth, kaolin,kieselguhr, etc., (3) ceramics, porcelain, crushed firebrick, bauxite;(4) refractory inorganic oxides such as alumina, titanium dioxide,zirconium dioxide, chromium oxide, beryllium oxide, vanadium oxide,cesium oxide, hafnium oxide, zinc oxide, magnesia, boria, thoria,silica-alumina, silica-magnesia, chromia-alumina, alumina-boria,silica-zirconia, etc.; (5) crystalline zeolitic aluminosilicates such asnaturally occurring or synthetically prepared mordenite and/orfaujasite, either in the hydrogen form or in a form which has beentreated with multivalent cations; (6) spinels such as MgAl₂ O₄, FeAl₂O₄, ZnAl₂ O₄, CaAl₂ O₄, and other like compounds having the formulaMO-Al₂ O₃ where M is a metal having a valence of 2; and (7) combinationsof elements from one or more of these groups. The preferred porouscarrier materials for use in the present invention are refractoryinorganic oxides, with best results obtained with an alumnina carriermaterial. Suitable alumina materials are the crystalline aluminas knownas gamma-, eta-, and theta-alumina, with gamma- or eta-alumina givingbest results. In addition, in some embodiments the alumina carriermaterial may contain minor proportions of other well known refractoryinorganic oxides such as silica, zirconia, magnesia, etc.; however, thepreferred support is substantially pure gamma- or eta-alumina. Preferredcarrier materials have an apparent bulk density of about 0.3 to about0.8 g/cc and surface area characteristics such that the average porediameter is about 20 to 300 Angstroms, the pore volume is about 0.1 toabout 1 cc/g and the surface area is about 100 to about 500 m² /g. Ingeneral, best results are typically obtained with a gamma-aluminacarrier material which is used in the form of spherical particleshaving: a relatively small diameter (i.e. typically about 1/16 inch), anapparent bulk density of about 0.3 to about 0.8 g/cc. a pore volume ofabout 0.4 ml/g. and a surface area of about 150 to about 250 m² /g.

The preferred alumina carrier material may be prepared in any suitablemanner and may be synthetically prepared or natural occurring. Whatevertype of alumina is employed, it may be activated prior to use by one ormore treatments including drying, calcination, steaming, etc., and itmay be in a form known as activated alumina, activated alumina ofcommerce, porous alumina, alumina gel, etc. For example, the aluminacarrier may be prepared by adding a suitable alkaline reagent, such asammonium hydroxide, to a salt of aluminum such as aluminum chloride,aluminum nitrate, etc., in an amount to form an aluminum hydroxide gelwhich upon drying and calcining is converted to alumina. The aluminacarrier may be formed in any desired shape such as spheres, pills,cakes, extrudates, powders, granules, tablets, etc., and utilized in anydesired size. For the purpose of the present invention a particularlypreferred form of alumina is the sphere, and alumina spheres may becontinuously manufactured by the well known oil drop method whichcomprises: forming an alumina hydrosol by any of the techniques taughtin the art and preferably by reacting alumina metal with hydrochloricacid, combining the resultant hydrosol with a suitable gelling agent anddropping the resultant mixture into an oil bath maintained at elevatedtemperatures. The droplets of the mixture remain in the oil bath untilthey set and form hydrogel spheres. The spheres are then continuouslywithdrawn from the oil bath and typically subjected to specific agingtreatments in oil and an ammoniacal solution to further improve theirphysical characteristics. The resulting aged and gelled particles arethen washed and dried at a relatively low temperature of about 300° F.to about 400° F. and subjected to a calcination procedure at atemperature of about 850° F. to about 1300° F. for a period of about 1to about 20 hours. This treatment effects conversion of the aluminahydrogel to the corresponding crystalline gamma-alumina. See theteachings of U.S. Pat. No. 2,620,314 for additional details.

Another particularly preferred alumina carrier material is synthesizedfrom a unique crystalline alumina powder which has been characterized inU.S. Pat. Nos. 3,852,190 and 4,012,313 as a byproduct from a Zieglerhigher alcohol synthesis reaction as described in Ziegler's U.S. Pat.No. 2,892,858. For purposes of simplification, the name "Ziegleralumina" is used herein to identify this material. It is presentlyavailable from the Conoco Chemical Division of Continental Oil Companyunder the trademark Catapal. This material is an extremely high purityalpha-alumina monohydrate (boehmite) which after calcination at a hightemperature has been shown to yield a high purity gamma-alumina. It iscommercially available in three forms: (1) Catapal SB--a spray driedpowder having a typical surface area of 250 m² /g; (2) Catapal NG--arotary kiln dried alumina having a typical surface are of 180 m² /g; and(3) Dispal M--a finely divided dispersable product having a typicalsurface area of about 185 m² /g. For purposes of the present invention,the preferred starting material is the spray dried powder, Catapal SB.This alpha-alumina monohydrate powder may be formed into a suitablecatalyst material according to any of the techniques known to thoseskilled in the catalyst carrier material forming art. Spherical carriermaterial particles can be formed, for example, from this Ziegler aluminaby: (1) coverting the alpha-alumina monohydrate powder into an aluminasol by reaction with a suitable peptizing acid and water and thereafterdropping a mixture of the resulting sol and a gelling agent into an oilbath to form spherical particles of an alumina gel which are easilyconverted to a gamma-alumina carrier material by known methods; (2)forming an extrudate from the powder by established methods andthereafter rolling the extrudate particles on a spinning disc untilspherical particles are formed which can then be dried and calcined toform the desired particles of spherical carrier material; and (3)wetting the powder with a suitable peptizing agent and thereafterrolling particles of the powder into spherical masses of the desiredsize in much the same way that children have been known to make parts ofsnowmen by rolling snowballs down hills covered with wet snow. Thisalumina powder can also be formed in any other desired shape or type ofcarrier material known to those skilled in the art such as rods, pills,pellets, tablets, granules, extrudates and the like forms by methodswell known to the practitioners of the catalyst carrier material formingart. The preferred type of carrier material for the present invention isa cylindrical extrudate having a diameter of about 1/32" to about 1/8"(especially about 1/16") and a length to diameter (L/D) ratio of about1:1 to about 5:1, with a L/D ratio of about 2:1 being especiallypreferred. The especially preferred extrudate form of the carriermaterial is preferably prepared by mixing the alumina powder with waterand a suitable peptizing agent such as nitric acid, acetic acid,aluminum nitrate and the like material until an extrudable dough isformed. The amount of water added to form the dough is typicallysufficient to give a loss on ignition (LOI) at 500° C. of about 45 to 65wt. %, with a value of about 55 wt. % being especially preferred. On theother hand, the acid addition rate is generally sufficient to provideabout 2 to 7 wt. % of the volatile free alumina powder used in the mix,with a value of about 3 to 4% being especially preferred. The resultingdough is then extruded through a suitably sized die to form extrudateparticles. These particles are then dried at a temperature of about 500°to 800° F. for a period of about 0.1 to about 5 hours and thereaftercalcined at a temperature of about 900° F. to about 1500° F. for aperiod of about 0.5 to about 5 hours to form the preferred extrudateparticles of the Ziegler alumina carrier material. In addition, in someembodiments of the present invention the Ziegler alumina carriermaterial may contain minor proportions of other well known refractoryinorganic oxides such as silica, titanium dioxide, zirconium dioxide,chromium oxide, beryllium oxide, vanadium oxide, cesium oxide, hafniumoxide, zinc oxide, iron oxide, cobalt oxide, magnesia, boria, thoria,and the like materials which can be blended into the extrudable doughprior to the extrusion of same. In the same manner crystalline zeoliticaluminosilicates such as naturally occurring or synthetically preparedmordenite and/or faujasite, either in the hydrogen form or in a formwhich has been treated with a multivalent cation, such as a rare earth,can be incorporated into this carrier material by blending finelydivided particles of same into the extrudable dough prior to extrusionof same. A preferred carrier material of this type is substantially pureZiegler alumina having an apparent bulk density (ABD) of about 0.6 to 1g/cc (especially an ABD of about 0.7 to about 0.85 g/cc), a surface areaof about 150 to about 280 m² /g (preferably about 185 to about 235 m²/g), and a pore volume of about 0.3 to about 0.8 cc/g.

A first essential ingredient of the subject catalyst is the platinumgroup component. That is, it is intended to cover the use of platinum,iridium, osmium, ruthenium, rhodium, palladium, or mixtures thereof as afirst component of the superactive catalytic composite. It is anessential feature of the present invention that substantially all ofthis platinum group component is uniformly dispersed throughout theporous carrier material in the elemental metallic state prior to theincorporation of the rhenium carbonyl ingredient. Generally, the amountof this component present in the form of catalytic composites is smalland typically will comprise about 0.01 to about 2 wt. % of finalcatalytic composite, calculated on an elemental basis. Excellent resultsare obtained when the catalyst contains about 0.05 to about 1 wt. % ofplatinum, iridium, rhodium or palladium metal. Particularly preferredmixtures of these platinum group metals preferred for use in thecomposite of the present invention are: (1) platinum and iridium and (2)platinum and rhodium.

The platinum group component may be incorporated in the porous carriermaterial in any suitable manner known to result in a relatively uniformdistribution of this component in the carrier material such ascoprecipitation or cogelation, ion-exchange or impregnation. Thepreferred method of preparing the catalyst involves the utilization of asoluble, decomposable compound of platinum group metal to impregnate thecarrier material in a relatively uniform manner. For example, thiscomponent may be added to the support by commingling the latter with anaqueous solution of chloroplatinic or chloroiridic or chloropalladicacid. Other water-soluble compounds or complexes of platinum groupmetals may be employed in impregnation solutions and include ammoniumchloroplatinate, bromoplatinic acid, platinum trichloride, platinumtetrachloride hydrate, platinum dichlorocarbonyl dichloride,dinitrodiaminoplatinum, sodium tetranitroplatinate (II), palladiumchloride, palladium nitrate, palladium sulfate, diamminepalladium (II)hydroxide, tetramminepalladium (II) chloride, hexamminerhodium chloride,rhodium carbonylchloride, rhodium trichloride hydrate, rhodium nitrate,sodium hexachlororhodate (III), sodium hexanitrorhodate (III), iridiumtribromide, iridium dichloride, iridium tetrachloride, sodiumhexanitroiridate (III), potassium or sodium chloroiridate, potassiumrhodium oxalate, etc. The utilization of a platinum, iridium, rhodium,or palladium chloride compound, such as chloroplatinic, chloroiridic, orchloropalladic acid or rhodium trichloride hydrate, is preferred sinceit facilitates the incorporation of both the platinum group componentand at least a minor quantity of the preferred halogen component in asingle step. Hydrogen chloride or the like acid is also generally addedto the impregnation solution in order to further facilitate theincorporation of the halogen component and the uniform distribution ofthe metallic components throughout the carrier material. In addition, itis generally preferred to impregnante the carrier material after it hasbeen calcined in order to minimize the risk of washing away the valuableplatinum group compound.

It is especially preferred to incorporate a halogen component into theplatinum group metal-containing porous carrier material prior to thereactions thereof with the rhenium carbonyl reagent. Although theprecise form of the chemistry of the association of the halogencomponent with the carrier material is not entirely known, it iscustomary in the art to refer to the halogen component as being combinedwith the carrier material, or with the platinum group metal in the formof the halide (e.g. as the chloride). This combined halogen may beeither fluorine, chlorine, iodine, bromine, or mixtures thereof. Ofthese, fluorine and, particularly, chlorine are preferred for thepurposes of the present invention. The halogen may be added to thecarrier material in any suitable manner, either during preparation ofthe support or before or after the addition of the platinum groupcomponent. For example, the halogen may be added, at any stage of thepreparation of the carrier material or to the calcined carrier material,as an aqueous solution of a suitable, decomposable halogen-containingcompound such as hydrogen fluoride, hydrogen chloride, hydrogen bromide,ammonium chloride, etc. The halogen component or a portion thereof, maybe combined with the carrier material during the impregnation of thelatter with the platinum group component; for example, through theutilization of a mixture of chloroplatinic acid and hydrogen chloride.In another situation, the alumina hydrosol which is typically utilizedto form a preferred alumina carrier material may contain halogen andthus contribute at least a portion of the halogen component to the finalcomposite. For reforming, the halogen will be typically combined withthe carrier material in an amount sufficient to to result in a finalcomposite that contains about 0.1 to about 3.5%, and preferably about0.5 to about 1.5%, by weight of halogen, calculated on an elementalbasis. In isomerization or hydrocracking embodiments, it is generallypreferred to utilize relatively larger amounts of halogen in thecatalyst--typically, ranging up to about 10 wt. % halogen calculated onan elemental basis, and more preferably, about 1 to about 5 wt. %. It isto be understood that the specified level of halogen component in theinstant superactive catalyst can be achieved or maintained during use inthe conversion of hydrocarbons by continuously or periodically adding tothe reaction zone a decomposable halogen-containing compound such as anorganic chloride (e.g. ethylene dichloride, carbon tetrachloride,t-butyl chloride) in an amount of about 1 to 100 wt. ppm. of thehydrocarbon feed, and preferably about 1 to 10 wt. ppm.

After the platinum group component is combined with the porous carriermaterial, the resulting platinum group metal containing carrier materialwill generally be dried at a temperature of about 200° F. to about 600°F. for a period of typically about 1 to about 24 hours or more andthereafter oxidized at a temperature of about 700° F. to about 1100° F.in an air or oxygen atmosphere for a period of about 0.5 to about 10 ormore hours or converts substantially all of the platinum group componentto the corresponding platinum group oxide. When the preferred halogencomponent is utilized in the present composition, best results aregenerally obtained when the halogen content of the platinum groupmetal-containing carrier material is adjusted during this oxidation stepby including a halogen or a halogen-containing compound in the air oroxygen atmosphere utilized. For purposes of the present invention, theparticularly preferred halogen is chlorine and it is highly recommendedthat the halogen compound utilized in this halogenation step be eitherhydrochloric acid or a hydrochloric acid producing substance. Inparticular, when the halogen component of the catalyst is chlorine, itis preferred to use a molar ratio of H₂ O to HCl of about 5:1 to about100:1 during at least a portion of the oxidation step which follows theplatinum group metal impregnation in order to adjust the final chlorinecontent of the catalyst to arrange of about 0.1 to about 3.5 wt. %.Preferably, the duration of this halogenation step is about 1 to 5 ormore hours.

A critical feature of the present invention involves subjecting theresulting oxidized, platinum group metal-containing, and typicallyhalogen-treated carrier material to a substantially water-free reductionstep before the incorporation of the rhenium component by means of therhenium carbonyl reagent. The importance of this reduction step comesfrom my observation that when an attempt is made to prepare the instantcatalytic composite without first reducing the platinum group component,no significant improvement in the platinum-rhenium catalyst system isobtained; put another way, it is my finding that it is essential for theplatinum group component to be well dispersed in the porous carriermaterial in the elemental metallic state prior to incorporation of therhenium component by the unique procedure of the present invention inorder for synergistic interaction of the rhenium carbonyl with thedispersed platinum group metal to occur according to the theories that Ihave previously explained. Accordingly, this reduction step is designedto reduce substantially all of the platinum group component to theelemental metallic state and to assure a relatively uniform and finallydivided dispersion of this metallic component throughout the porouscarrier material. Preferably a substantially pure and dry hydrogenstream (by the use of the word "dry" I mean that it contains less than20 vol. ppm. water and preferably less than 5 vol. ppm. water) is usedas the reducing agent in this step. The reducing agent is contacted withthe oxidized, platinum group metal-containing carrier material atconditions including a reduction temperature of about 450° F. to about1200° F. for a period of about 0.5 to about 10 or more hours selected toreduce substantially all of the platinum group component to theelemental metallic state. Once this condition of finally divideddispersed platinum group metal in the porous carrier material isachieved, it is important that environments and/or conditions that coulddisturb or change this condition be avoided; specifically, I much preferto maintain the freshly reduced carrier material containing the platinumgroup metal under a blanket of inert gas to avoid any possibility ofcontamination of same either by water or by oxygen.

A second essential ingredient of the present superactive catalyticcomposite is a rhenium component which I have chosen to characterize asa pyrolyzed rhenium carbonyl in order to emphasize that the rheniummoiety of interest in my invention is the rhenium produced bydecomposing a rhenium carbonyl in the presence of a finally divideddispersion of a platinum group metal and in the absence of materialssuch as oxygen or water which could interfere with the basic desiredinteraction of the rhenium carbonyl component with the platinum groupmetal component as previously explained. In view of the fact that all ofthe rhenium contained in a rhenium carbonyl compound is present in theelemental metallic state, an essential requirement of my invention isthat the resulting reaction product of the rhenium carbonyl compound orcomplex with the platinum group metal loaded carrier material is notsubjected to conditions which could in any way interfere with themaintenance of the rhenium moiety in the elemental metallic state;consequently, avoidance of any conditions which would tend to cause theoxidation of any portion of the rhenium ingredient or of the platinumgroup ingredient is a requirement for full realization of thesynergistic interaction enabled by the present invention. This rheniumcomponent may be utilized in the resulting composite in any amount thatis catalytically effective with the preferred amount typicallycorresponding to about 0.01 to about 5 wt. % thereof, calculated on anelemental rhenium basis. Best results are oridinarily obtained withabout 0.05 to about 1 wt. % rhenium. The traditional rule forrhenium-platinum catalyst system is that best results are achieved whenthe amount of the rhenium component is set as a function of the amountof the platinum group component also hold for my composition;specifically, I find that best results with a rhenium to platinum groupmetal atomic ratio of about 0.1:1 to about 10:1, with an especiallyuseful range comprising about 0.2:1 to about 5:1 and with superiorresults achieved at an atomic ratio of rhenium to platinum group metalof about 1:1.

The rhenium carbonyl ingredient may be reacted with the reduced platinumgroup metal-containing porous carrier material in any suitable mannerknown to those skilled in the catalyst formulation art which results inrelatively good contact between the rhenium carbonyl complex and theplatinum group component contained in the porous carrier material. Oneacceptable procedure for incorporating the rhenium carbonyl compoundinto the composite involves sublimating the rhenium carbonyl complexunder conditions which enable it to pass into the vapor phase withoutbeing decomposed and thereafter contacting the resulting rheniumcarbonyl sublimate with the platinum group metal-containing porouscarrier material under conditions designed to achieve intimate contactof the carbonyl reagent with the platinum group metal dispersed on thecarrier material. Typically this procedure is performed under vacuum ata temperature of about 70° to about 250° F. for a period of timesufficient to react the desired amount of rhenium with the carriermaterial. In some cases an inert carrier gas such as nitrogen can beadmixed with the rhenium carbonyl sublimate in order to facilitate theintimate contacting of same with the platinum-loaded porous carriermaterial. A particularly preferred way of accomplishing this rheniumcarbonyl reaction step is an impregnation procedure wherein theplatinum-loaded porous carrier material is impregnated with a suitablesolution containing the desired quantity of the rhenium carbonylcomplex. For purposes of the present invention, organic solutions arepreferred, although any suitable solution may be utilized as long as itdoes not interact with the rhenium carbonyl and cause decomposition ofsame. Obviously the organic solution should be anhydrous in order toavoid detrimental interaction of water with the rhenium carbonylcompound. Suitable solvents are any of the commonly available organicsolvents such as one of the available ethers, alcohols, ketones,aldehydes, paraffins, naphthenes and aromatic hydrocarbons, for example,acetone, acetyl acetone, benzaldehyde, pentane, hexane, carbontetrachloride, methyl isopropyl ketone, benzene, n-butylether, diethylether, ethylene glycol, methyl isobutyl ketone, disobutyl ketone and thelike organic solvents. Best results are ordinarily obtained when thesolvent is acetone; consequently, the preferred impregnation solution isrhenium carbonyl dissolved in anhydrous acetone. The rhenium carbonylcomplex suitable for use in the present invention may be either the purerhenium carbonyl itself or a substituted rhenium carbonyl such as therhenium carbonyl halides including the chlorides, bromides, and iodidesand the like substituted rhenium carbonyl complexes. After impregnationof the carrier material with the rhenium carbonyl component, it isimportant that the solvent be removed or evaporated from the catalystprior to decomposition of the rhenium carbonyl component by means of thehereinafter described pyrolysis step. The reason for removal of thesolvent is that I believe that the presence of organic materials such ashydrocarbons or derivatives of hydrocarbons during the rhenium carbonylpyrolysis step is highly detrimental to the synergistic interactionassociated with the present invention. This solvent is removed bysubjecting the rhenium carbonyl impregnated carrier material to atemperature of about 100° F. to about 250° F. in the presence of aninert gas or under a vacuum condition until substantially no furthersolvent is observed to come off the impregnated material. In thepreferred case where acetone is used as the impregnation solvent, thisdrying of the impregnated carrier material typically takes about onehalf hour at a temperature of about 225° F. under moderate vacuumconditions.

After the rhenium carbonyl component is incorporated into theplatinum-loaded porous carrier material, the resulting composite is,pursuant to the present invention, subjected to pyrolysis conditionsdesigned to decompose substantially all of the rhenium carbonylmaterial, without oxidizing either the platinum group or the decomposedrhenium carbonyl component. This step is preferably conducted in anatmosphere which is substantially inert to the rhenium carbonyl such asin a nitrogen or noble gas-containing atmosphere. Preferably thispyrolysis step takes place in the presence of a substantially pure anddry hydrogen stream. It is of course within the scope of the presentinvention to conduct the pyrolysis step under vacuum conditions. It ismuch preferred to conduct this step in the substantial absence of freeoxygen and substances that could yield free oxygen under the conditionsselected. Likewise it is clear that best results are obtained when thisstep is performed in the total absence of water and of hydrocarbons andother organic materials. I have obtained best results in pyrolyzingrhenium carbonyl while using an anhydrous hydrogen stream at pyrolysisconditions including a temperature of about 300° F. to about 900° F. ormore, preferably about 400° F. to about 750° F., a gas hourly spacevelocity of about 250 to about 1500 hr.⁻¹ for a period of about 0.5 toabout 5 or more hours until no further evolution of carbon monoxide isnoted. After the rhenium carbonyl component has been pyrolyzed, it is amuch preferred practice to maintain the resulting catalytic composite inan inert environment (i.e. a nitrogen or the like inert gas blanket)until the catalyst is loaded into a reaction zone for use in theconversion of hydrocarbons.

The resulting pyrolyzed catalytic composite may, in some cases, bebeneficially subjected to a presulfiding step designed to incorporate inthe catalytic composite from about 0.01 to about 1 wt. % sulfurcalculated on an elemental basis. Preferably, this presulfidingtreatment takes place in the presence of hydrogen and a suitabledecomposable sulfer-containing compound such as hydrogen sulfide, lowermolecular weight mercaptans, organic sulfides, etc. Typically, thisprocedure comprises treating the pyrolyzed catalyst with a sulfiding gassuch as a mixture of hydrogen and hydrogen sulfide containing about 10moles of hydrogen per mole of hydrogen sulfide at conditions sufficientto effect the desired incorporation of sulfur, generally including atemperature ranging from about 50° F. up to about 1000° F. It isgenerally a preferred practice to perform this presulfiding step undersubstantially water-free and oxygen-free conditions. It is within thescope of the present invention to maintain or achieve the sulfided stateof the present catalyst during use in the conversion of hydrocarbons bycontinuously or periodically adding a decomposable sulfur-containingcompound, selected from the above mentioned hereinbefore, to the reactorcontaining the superactive catalyst in an amount sufficient to provideabout 1 to 500 wt. ppm, preferably about 1 to about 20 wt. ppm. ofsulfur, based on hydrocarbon charge. According to another mode ofoperation, this sulfiding step may be accomplished during the pyrolysisstep by utilizing a rhenium carbonyl reagent which has asulfur-containing ligand or by adding H₂ S to the hydrogen stream whichis preferably used therein.

In embodiments of the present invention wherein the instant superactivemultimetallic catalytic composite is used for the dehydrogenation ofdehydrogenatable hydrocarbons or for the hydrogenation of hydrogenatablehydrocarbons, it is oridinarily a preferred practice to include analkali or alkaline earth metal component in the composite beforeaddition of the rhenium carbonyl component and to minimize or eliminatethe preferred halogen component. More precisely, this optionalingredient is selected from the group consisting of the compounds of thealkali metals--cesium, rubidium, potassium, sodium, and lithium--and thecompounds of the alkaline earth metals--calcium, strontium, barium, andmagnesium. Generally, good results are obtained in these embodimentswhen this component constitutes about 0.1 to about 5 wt. % of thecomposite, calculated on an elemental basis. This optional alkali oralkaline earth metal component can be incorporated into the composite inany of the known ways, with impregnation with an aqueous solution of asuitable water-soluble, decomposable compound being preferred.

An optional ingredient for the superactive multimetallic catalyst of thepresent invention is a Friedel-Crafts metal halide component. Thisingredient is particularly useful in hydrocarbon conversion embodimentsof the present invention wherein it is preferred that the catalystutilized has a strong acid or cracking function associatedtherewith--for example, an embodiment wherein the hydrocarbons are to behydrocracked or isomerized with the catalyst of the present invention.Suitable metal halides of the Friedel-Crafts type include aluminumchloride, aluminum bromide, ferric chloride, ferric bromide, zincchloride, and the like compounds, with the aluminum halides andparticularly aluminum chloride ordinarily yielding best results.Generally, this optional ingredient can be incorporated into thecomposite of the present invention by any of the conventional methodsfor adding metallic halides of this type and either prior to or afterthe rhenium carbonyl reagent is added thereto; however, best results areordinarily obtained when the metallic halide is sublimed onto thesurface of the carrier material after the rhenium is added theretoaccording to the preferred method disclosed in U.S. Pat. No. 2,999,074.The component can generally be utilized in any amount which iscatalytically effective, with a value selected from the range of about 1to about 100 wt. % of the carrier material generally being preferred.

According to the present invention, a hydrocarbon charge stock andhydrogen are contacted with the instant superactive pyrolyzedmultimetallic catalyst in a hydrocarbon conversion zone. This contactingmay be accomplished by using the catalyst in a fixed bed system, amoving bed system, a fluidized bed system, or in a batch type operation;however, in view of the danger of attrition losses of the valuablecatalyst and of well known operational advantages, it is preferred touse either a fixed bed system or a dense-phase moving bed system such asis shown in U.S. Pat. No. 3,725,249. It is also comtemplated that thecontacting step can be performed in the presence of a physical mixtureof particles of the catalyst of the present invention and particles of aconventional dual-function catalyst of the prior art. In a fixed bedsystem, a hydrogen-rich gas and the charge stock are preheated by anysuitable heating means to the desired reaction temperature and then arepassed into a conversion zone containing a fixed bed of the instantsuperactive acidic multimetallic catalyst. It is, of course, understoodthat the conversion zone may be one or more separate reactors withsuitable means therebetween to ensure that the desired conversiontemperature is maintained at the entrance to each reactor. It is alsoimportant to note that the reactants may be contacted with the catalystbed in either upward, downward, or radial flow fashion with the latterbeing preferred. In addition, the reactants may be in the liquid phase,a mixed liquid-vapor phase, or a vapor phase when they contact thecatalyst, with best results obtained in the vapor phase.

In the case where the superactive multimetallic catalyst of the presentinvention is used in a reforming operation, the reforming system willtypically comprise a reforming zone containing one or more fixed beds ordense-phase moving beds of the catalysts. In a multiple bed system, itis, of course, within the scope of the present invention to use thepresent catalyst in less than all of the beds with a conventionaldual-function catalyst being used in the remainder of the beds. Thisreforming zone may be one or more separate reactors with suitableheating means therebetween to compensate for the endothermic nature ofthe reactions that take place in each cataylst bed. The hydrocarbon feedstream that is charged to this reforming system will comprisehydrocarbon fractions containing naphthenes and paraffins that boilwithin the gasoline range. The preferred charge stocks are thoseconsisting essentially of naphthenes and paraffins, although in somecases aromatics and/or olefins may also be present. The preferred classincludes straight run gasolines, natural gasolines, synthetic gasolines,partially reformed gasolines, and the like. On the other hand, it isfrequently advantageous to charge thermally or catalytically crackedgasolines or higher boiling fractions thereof. Mixtures of straight runand cracked gasolines can also be used to advantage. The gasoline chargestock may be a full boiling gasoline having an initial boiling point offrom about 50° F. to about 150° F. and an end boiling point within therange of from about 325° F. to about 425° F., or may be a selectedfraction thereof which generally will be a higher boiling fractioncommonly referred to as a heavy naphtha--for example, a naphtha boilingin the range of C₇ to 400° F. In some cases, it is also advantageous tocharge pure hydrocarbons or mixtures of hydrocarbons that have beenextracted from hydrocarbon distillates--for example, straight-chainparaffins--which are to be converted to aromatics. It is preferred thatthese charge stocks be treated by conventional catalytic pretreatmentmethods such as hydrorefining, hydrotreating, hydrodesulfurization,etc., to remove substantially all sulfurous, nitrogenous, andwater-yielding contaminants therefrom and to saturate any olefins thatmay be contained therein.

In other hydrocarbon conversion embodiments, the charge stock will be ofthe conventional type customarily used for the particular kind ofhydrocarbon conversion being effected. For example, in a typicalisomerization embodiment, the charge stock can be a paraffinic stockrich in C₄ to C₈ normal paraffins, or a normal butane-rich stock, or ann-hexane-rich stock, or a mixture of xylene isomers, or anolefin-containing stock, etc. In a dehydrogenation embodiment, thecharge stock can be any of the known dehydrogenatable hydrocarbons suchas an aliphatic compound containing 2 to 30 carbon atoms per molecule, aC₄ to C₃₀ normal paraffin, a C₈ to C₁₂ alkylaromatic, a naphthene, andthe like. In hydrocracking embodiments, the charge stock will betypically a gas oil, heavy cracked cycle oil, etc. In addition,alkylaromatics, olefins, and naphthenes can be conveniently isomerizedby using the catalyst of the present invention. Likewise, purehydrocarbons or substantially pure hydrocarbons can be converted to morevaluable products by using the acidic multimetallic catalyst of thepresent invention in any of the hydrocarbon conversion processes, knownto the art, that use a dual-function catalyst.

In a reforming embodiment, it is generally preferred to utilize thesuperactive pyrolyzed multimetallic catalytic composite in asubstantially water-free environment. Essential to the achievement ofthis condition in the reforming zone is the control of the water levelpresent in the charge stock and the hydrogen stream which is beingcharged to the zone. Best results are ordinarily obtained when the totalamount of water entering the conversion zone from any source is held toa level less than 50 ppm. and preferably less than 20 ppm. expressed asweight of equivalent water in the charge stock. In general, this can beaccomplished by careful control of the water present in the charge stockand in the hydrogen stream. The charge stock can be dried by using anysuitable drying means known to the art, such as a conventional solidadsorbent having a high selectivity for water, for instance, sodium orcalcium crystalline aluminosilicates, silica gel, activated alumina,molecular sieves, anhydrous calcium sulfate, high surface area sodium,and the like adsorbents. Similarly, the water content of the chargestock may be adjusted by suitable stripping operations in afractionation column or like device. And in some cases, a combination ofadsorbent drying and distillation drying may be used advantageously toeffect almost complete removal of water from the charge stock. In anespecially preferred mode of operation, the charge stock is dried to alevel corresponding to less than 5 wt. ppm. of water equivalent. Ingeneral, it is preferred to maintain the hydrogen stream entering thehydrocarbon conversion zone at a level of about 10 vol. ppm. of water orless and most preferably about 5 vol. ppm. or less. If the water levelin the hydrogen stream is too high, drying of same can be convenientlyaccomplished by contacting the hydrogen stream with a suitable desiccantsuch as those mentioned above.

In the reforming embodiment, an effluent stream is withdrawn from thereforming zone and passed through a cooling means to a separation zone,typically maintained at about 25° F. to 150° F., wherein a hydrogen-richgas stream is separated from a high octane liquid product stream,commonly called an unstabilized reformate. When the water level in thehydrogen stream is outside the range previously specified, at least aportion of this hydrogen-rich gas stream is withdrawn from theseparating zone and passed through an adsorption zone containing anadsorbent selective for water. The resultant substantially water-freehydrogen stream can then be recycled through suitable compressing meansback to the reforming zone. The liquid phase from the separating zone istypically withdrawn and commonly treated in a fractionating system inorder to adjust the butane concentration, thereby controlling front-endvolatility of the resulting reformate.

The operating conditions utilized in the numerous hydrocarbon conversionembodiments of the present invention are in general those customarilyused in the art for the particular reaction, or combination ofreactions, that is to be effected. For instance, alkylaromatic, olefin,and paraffin isomerization conditions include: a temperature of about32° F. to about 1000° F. and preferably from about 75° F. to about 600°F., a pressure of atmospheric to about 100 atmospheres, a hydrogen tohydrocarbon mole ratio of about 0.5:1 to about 20:1, and an LHSV(calculated on the basis of equivalent liquid volume of the charge stockcontacted with the catalyst per hour divided by the volume of conversionzone containing catalyst and expressed in units of hr.⁻¹) of about 0.2to 10. Dehydrogenation conditions include: a temperature of about 700°F. to about 1250° F., a pressure of about 0.1 to about 10 atomospheres,a liquid hourly space velocity of about 1 to 40, and a hydrogen tohydrocarbon mole ratio of about 1:1 to 20:1. Likewise, typicalhydrocracking conditions include: a pressure of about 500 psig. to about3000 psig., a temperature of about 400° F. to about 900° F., an LHSV ofabout 0.1 to about 10, and hydrogen circulation rates of about 1000 to10,000 SCF per barrel of charge.

In the reforming embodiment of the present invention, the pressureutilized is selected from the range of about 0 psig. to about 1000psig., with the preferred pressure being about 50 psig. to about 600psig. Particularly good results are obtained at low or moderatepressure; namely, a pressure of about 100 to 450 psig. In fact, it is asingular advantage of the present invention that it allows stableoperation at lower pressure than have heretofore been successfullyutilized in so-called "continuous" reforming systems (i.e. reforming forperiods of about 15 to about 200 or more barrels of charge per pound ofcatalyst without regeneration) with conventional platinum-rheniumcatalyst systems. In other, words, the superactive pyrolyzedmultimetallic catalyst of the present invention allowed the operation ofa continuous reforming system to be conducted at lower pressure (i.e.100 to about 350 psig.) for about the same or better catalyst cycle lifebefore regeneration as has been heretofore realized with conventionalplatinum-rhenium catalysts at higher pressure (i.e. 300 to 600 psig.).On the other hand, the extraordinary activity and activity-stabilitycharacteristics of the catalyst of the present invention relative to aconventional platinum-rhenium catalyst enables reforming operationsconducted at pressures of 300 to 600 psig. to achieve substantiallyincreased catalyst cycle life before regeneration.

The temperature required for reforming with the instant catalyst ismarkedly lower than that required for a similar reforming operationusing a high quality platinum-rhenium catalyst of the prior art. Thissignificant and desirable feature of the present invention is aconsequence of the superior activity of the superactive pyrolyzedmultimetallic catalyst of the present invention for the octane-upgradingreactions that are preferably induced in a typical reforming operation.Hence, the present invention requires a temperature in the range of fromabout 775° F. to about 1100° F. and preferably about 850° F. to about1050° F. As is well known to those skilled in the continuous reformingart, the initial selection of the temperature within this broad range ismade primarily as a function of the desired octane of the productreformate considering the characteristics of the charge stock and of thecatalyst. Ordinarily, the temperature then is thereafter slowlyincreased during the run to compensate for the inevitable deactivationthat occurs to provide a constant octane product. Therefore, it is afeature of the present invention that not only is the initialtemperature requirement lower, but also the rate at which thetemperature is increased in order to maintain a constant octane productis for the instant catalyst system at least as good as if not betterthan for an equivalent operation with a high quality platinum-rheniumcatalyst system of the prior art; for instance, a catalyst prepared inaccordance with the teachings of U.S. Pat. No. 3,415,737. Moreover, forthe catalyst of the present invention, the average C₅ + yield and theC₅ + yield stability are equal to or better than for this high qualitybimetallic reforming catalyst of the prior art. The superior activity,selectivity and stability characteristics of the instant catalyst can beutilized in a number of highly beneficial ways to enable increasedperformance of a catalytic reforming process relative to that obtainedin a similar operation with a platinum-rhenium catalyst of the priorart, some of these are: (1) Octane number of C₅ + product can beincreased without sacrificing average C₅ + yield and/or catalyst runlength. (2) The duration of the process operation (i.e. catalyst runlength or cycle life) before regeneration becomes necessary can beincreased. (3) C₅ + yield can be further increased by lowering averagereactor pressure with no change in catalyst run length. (4) Investmentcosts can be lowered without any sacrifice in cycle life or in C₅ +yield by lowering recycle gas requirements thereby saving on capitalcost for compressor capacity or by lowering initial catalyst loadingrequirements thereby saving on cost of catalyst and on capital cost ofthe reactors. (5) Throughput can be increased significantly at nosacrifice in catalyst cycle life or in C₅ + yield if sufficient heatercapacity is available.

The reforming embodiment of the present invention also typicallyutilizes sufficient hydrogen to provide an amount of about 1 to about 20moles to hydrogen per mole to hydrocarbon entering the reforming zone,with excellent results being obtained when about 2 to about 6 moles ofhydrogen are used per mole of hydrocarbon. Likewise, the liquid hourlyspace velocity (LHSV) used in reforming is selected from the range ofabout 0.1 to about 10, with a value in the range of about 1 to about 5being preferred. In fact, it is a feature of the present invention thatit allows operations to be conducted at higher LHSV than normally can bestably achieved in a continuous reforming process with a high qualityplatinum-rhenium reforming catalyst of the prior art. This last featureis of immense economic significance because it allows a continuousreforming process to operate at the same throughput level with lesscatalyst inventory or at greatly increased throughput level with thesame catalyst inventory than that heretofore used with conventionalplatinum-rhenium reforming catalyst at no sacrifice in catalyst lifebefore regeneration.

The following examples are given to illustrate further the preparationof the superactive pyrolyzed multimetallic catalytic composite of thepresent invention and the use thereof in the conversion of hydrocarbons.It is understood that the examples are intended to be illustrativerather than restrictive.

EXAMPLE I

An alumina carrier material comprising 1/16 inch spheres was preparedby: forming an aluminum hydroxyl chloride sol by dissolvingsubstantially pure aluminum pellets in a hydrochloric acid solution,adding hexamethylenetetramine to the resulting alumina sol, gelling theresulting solution by dropping it into an oil bath to form sphericalparticles of an alumina hydrogel, aging and washing the resultingparticles and finally drying and calcining the aged and washed particlesto form spherical particles of gamma-alumina containing about 0.3 wt. %combined chloride. Additional details as to this method of preparing thepreferred gamma-alumina carrier material are given in the teachings ofU.S. Pat. No. 2,620,314.

An aqueous impregnation solution containing chloroplatinic acid andhydrogen chloride was then prepared. The alumina carrier material wasthereafter admixed with the impregnation solution. The amount of themetallic reagent contained in this impregnation solution was calculatedto result in a final composite containing, on an elemental basis, 0.375wt. % platinum. In order to insure uniform dispersion of the platinumcomponent throughout the carrier material, the amount of hydrogenchloride used in this impregnation solution was about 2 wt. % of thealumina particles. This impregnation step was performed by adding thecarrier material particles to the impregnation mixture with constantagitation. In addition, the volume of the solution was approximately thesame as the bulk volume of the alumina carrier material particles sothat all of the particles were immersed in the impregnation solution.The impregnation mixture was maintained in contact with the carriermaterial particles for a period of about 1/2 to about 3 hours at atemperature of about 70° F. Thereafter, the temperature of theimpregnation mixture was raised to about 225° F. and the excess solutionwas evaporated in a period of about 1 hour. The resulting driedimpregnated particles were then subjected to an oxidation treatment in adry air stream at a temperature of about 975° F. and a GHSV of about 500hr.⁻¹ for about 1/2 hour. This oxidation step was designed to convertsubstantially all of the platinum ingredient to the correspondingplatinum oxide form. The resulting oxidized spheres were subsequentlycontacted in a halogen treating step with an air stream containing H₂ Oand HCl in a mole ratio of about 30:1 for about 2 hours at 975° F. and aGHSV of about 500 hr.⁻¹ in order to adjust the halogen content of thecatalyst particles to a value of about 1 wt. %. The halogen-treatedspheres were thereafter subjected to a second oxidation step with a dryair stream at 975° F. and a GHSV of 500 hr.⁻¹ for an additional periodof about 1/2 hour.

The resulting oxidized, halogen-treated, platinum-containing carriermaterial particles were then subjected to a dry reduction treatmentdesigned to reduce substantially all of the platinum component to theelemental state and to maintain a uniform dispersion of this componentin the carrier material. This reduction step was accomplished bycontacting the particles with a hydrocarbon-free, dry hydrogen streamcontaining less than 5 vol. ppm. H₂ O at a temperature of about 1050°F., a pressure slightly above atmospheric, a flow rate of hydrogenthrough the particles corresponding to a GHSV of about 400 hr.⁻¹ and fora period of about one hour.

Rhenium carbonyl complex, Re₂ (CO)₁₀, was thereafter dissolved in ananhydrous acetone solvent in order to prepare the rhenium carbonylsolution which was used as the vehicle for reacting rhenium carbonylwith the carrier material containing the uniformly dispersed platinummetal. The amount of the complex used was selected to result in afinished catalyst containing about 0.375 wt. % carbonyl-derived rheniummetal. The resulting rhenium carbonyl solution was then contacted underappropriate impregnation conditions with the reduced,platinum-containing alumina carrier material resulting from thepreviously described reduction step. The impregnation conditionsutilized were: a contact time of about one half to about three hours, atemperature of about 70° F. and a pressure of about atmospheric. It isimportant to note that this impregnation step was conducted under anitrogen blanket so that oxygen was excluded from the environment andalso this step was performed under anhydrous conditions. Thereafter theacetone solvent was removed under flowing nitrogen at a temperature ofabout 175° F. for a period of about one hour. The resulting dry rheniumcarbonyl impregnated particles were then subjected to a pyrolysis stepdesigned to decompose the carbonyl compound. This step involvedsubjecting the carbonyl impregnated particles to a flowing hydrogenstream at a first temperature of about 230° F. for about one half hourat a GHSV of about 600 hr.⁻¹ and at atmospheric pressure. Thereafter inthe second portion of the pyrolysis step the temperature of theimpregnated particles was raised to about 575° F. for an additionalinterval of about one hour until the evolution of CO was no longerevident. The resulting catalyst was then maintained under a nitrogenblanket until it was loaded into the reactor in the subsequentlydescribed reforming test.

A sample of the resulting pyrolyzed rhenium carbonyl andplatinum-containing catalytic composite was analyzed and found tocontain, on an elemental basis, about 0.375 wt. % platinum, about 0.375wt. % rhenium, and about 1.0 wt. % chloride. The resulting catalyst wasthen divided into two separate portions, the first of which ishereinafter referred to as Catalyst A and the second of which ishereinafter named Catalyst B.

EXAMPLE II

In order to compare the superactive acidic multimetallic catalyticcomposite of the present invention with a platinum-rhenium catalystsystem of the prior art in a manner calculated to bring out thebeneficial interaction of the pyrolyzed rhenium carbonyl component withthe platinum component, a comparison test was made between the catalystof the present invention prepared in accordance with Example I, CatalystA, and a control catalyst, which was a bimetallic reforming catalyst ofthe prior art which is similar to the catalyst exemplified in theteachings of Kluksdahl's U.S. Pat. No. 3,415,737. The control catalystis hereinafter called Catalyst C and was a conventional combination ofplatinum, rhenium and chloride with an alumina which was prepared byco-impregnation of platinum and rhenium using an impregnation solutioncontaining the required amounts of chloroplatinic acid, perrhenic acidand hydrochloric acid. This control catalyst contained these metals inexactly the same amounts as the catalyst of the present invention; thatis, the catalyst contained 0.375 wt. % platinum, 0.375 wt. % rhenium andabout 1.0 wt. % chloride. Catalyst C is thus representative of theplatinum-rhenium bimetallic catalyst systems of the prior art.

These catalysts were then separately subjected to a high stressaccelerated catalytic reforming evaluation test designed to determine ina relatively short period of time their relative activity, selectivity,and stability characteristics in a process for reforming a relativelylow-octane gasoline fraction. In all tests the same charge stock wasutilized and its pertinent characteristics are set forth in Table I.

This accelerated reforming test was specifically designed to determinein a very short period of time whether the catalyst being evaluated hassuperior characteristics for use in a high severity reforming operation

                  TABLE I                                                         ______________________________________                                         Analysis of Charge Stock                                                     ______________________________________                                        Gravity, API at 60° F.                                                                          59.1                                                 Distillation Profile, ° F.                                             Initial Boiling Point    210                                                   5% Boiling Point        220                                                  10% Boiling Point        230                                                  30% Boiling Point        244                                                  50% Boiling Point        278                                                  70% Boiling Point        292                                                  90% Boiling Point        316                                                  95% Boiling Point        324                                                  End Boiling Point        356                                                  Chloride, wt. ppm.       0.2                                                  Nitrogen, wt. ppm        0.1                                                  Sulfur, wt. ppm.         0.1                                                  Water, wt. ppm.          10                                                   Octane Number, F-1 clear 35.6                                                 Paraffins, vol. %        67.4                                                 Naphthenes, vol. %       23.1                                                 Aromatics, vol. %        9.5                                                  ______________________________________                                    

Each run consisted of a series of evaluation periods of 24 hours, eachof these periods comprises a 12-hour line-out period followed by a12-hour test period during which the C₅ + product reformate from theplant was collected and analyzed. The test runs for the Catalysts A andB were performed at identical conditions which comprises a LHSV of 2.0hr.⁻¹, a pressure of 300 psig., a 3.5:1 gas to oil ratio, and an inletreactor temperature which was continuously adjusted throughout the testin order to achieve and maintain a C₅ + target research octane of 100.

Both test runs were performed in a pilot plant scale reforming unitcomprising a reactor containing a fixed bed of the catalyst undergoingevaluation, a hydrogen separation zone, a debutanizer column, andsuitable heating means, pumping means, condensing means, compressingmeans, and the like conventional equipment. The flow scheme utilized inthis plant involves commingling a hydrogen recycle stream with thecharge stock and heating the resulting mixture to the desired conversiontemperature. The heated mixture is then passed downflow into a reactorcontaining the catalyst undergoing evaluation as a stationary bed. Aneffluent stream is then withdrawn from the bottom of the reactor, cooledto about 55° F. and passed to a gas-liquid separation zone wherein ahydrogen-rich gaseous phase separates from a liquid hydrocarbon phase. Aportion of the gaseous phase is then continuously passed through a highsurface area sodium scrubber and the resulting substantially water-freeand sulfur-free hydrogen-containing gas stream is returned to thereactor in order to supply the hydrogen recycle stream. The excessgaseous phase from the separation zone is recovered as thehydrogen-containing product stream (commonly called "excess recyclegas"). The liquid phase from the separation zone is withdrawn therefromand passed to a debutanizer column wherein light ends (i.e. C₁ to C₄)are taken overhead as debutanizer gas and C₅ + reformate streamrecovered as the principal bottom product.

The results of the separate tests performed on the superactive catalystsof the present invention, Catalysts A and B, and the control catalyst,Catalyst C, are presented in FIGS. 1, 2 and 3 as a function of time asmeasured in days on oil. The results for catalyst A are represented bythe line connecting the circles, for catalyst B, the line connecting thetriangles and for catalyst C, the dotted line. FIG. 1 shows graphicallythe relationship between C₅ + yields expressed as liquid volume percent(LV%) of the charge for each of the catalysts. FIG. 2 on the other handplots the observed hydrogen purity in mole percent of the recycle gasstream for each of the catalysts. And finally, FIG. 3 tracks inletreactor temperature necessary for each catalyst to achieve a targetresearch octane number of 100.

Referring now to the results of the comparison test presented in FIGS.1, 2 and 3 for Catalysts A and C, it is immediately evident that thesuperactive multimetallic catalytic composite of the present inventionsubstantially outperformed the conventional platinum-rhenium controlcatalyst in the areas of activity and activity stability. Turning toFIG. 1 it can be ascertained that the C₅ + selectivity for Catalyst Awas slightly below that exhibited for Catalyst C with similar yieldstability. This minor sacrifice in C₅ + yield can be compensated for byincreasing the severity level as will be explained in conjunction withthe discussion of the results for Catalyst B. Hydrogen selectivities forthese two catalysts are given in FIG. 2 and it is clear from the datathat there is a small sacrifice in hydrogen selectivity that accompaniesthe advance of the present invention; I attribute this diminishedhydrogen selectivity to the tremendous increase in metals activitymanifested by my unique platinum-rhenium catalyst system. Put anotherway, it is clear from the data for hydrogen selectivities that the novelplatinum-rhenium system of the present invention is producing much moremetal activity than the platinum-rhenium catalyst system of the priorart; consequently, hydrogenolysis activity is at a high level with thecorresponding increase in light-end hydrocarbons. This diminishedselectivity for hydrogen is a commonly observed phenomenon for extremelyhigh activity catalyst systems. The data presented in FIG. 3 immediatelyhighlights the surprising and significant difference in activity betweenthe two catalyst systems. From the data presented in FIG. 3 it is clearthat Catalyst A was consistently 25° F. to 30° F. more active than thecontrol catalyst when the two catalysts were run at exactly the sameconditions. This is an extremely surprising result because of theinability of the platinum-rhenium catalyst systems of the prior art toshow any advance in activity over the traditional platinum system; thusit is immediately apparent from the data in FIG. 3 that a significantand unexpected improvement in activity characteristics is a principaladvantage of the platinum-rhenium catalyst of the present invention.Applying the well known rule of thumb that the rate of reactionapproximately doubles for every 20° F. change in reaction temperature,it is manifest that Catalyst A is approximately twice as active asCatalyst C. This significant advance in activity characteristics iscoupled with activity-stability for Catalyst A relative to Catalyst Cwhich is at least as good as or slightly better than the prior artcatalyst system. The activity stability is perhaps best judged byexamining the slopes of the two curves for Catalyst A and Catalyst Cplotted in FIG. 3. In sum, the cumulative effect of the data plotted inFIGS. 1, 2 and 3 indicate that the catalyst system of the presentinvention is significantly more active than the control catalyst andthat this dramatic increase in activity is accomplished at some minorsacrifice in hydrogen purity and in C₅ + yield.

This deficiency in C₅ + yield can be compensated for, as is well knownto those skilled in the art, by an adjustment in the severity levelwhich is easily accomplished in view of the tremendous increase inactivity manifested by Catalyst A. In order to prove this point for thiscatalyst system, the data for Catalyst B, a catalyst of the presentinvention, is also presented in FIGS. 1, 2 and 3 plotted as a functionof catalyst life measured in days on oil. The only difference betweenthe runs for Catalyst A and C and that for Catalyst B is a slightmodification in severity level which is designed to trade off some ofthe superactivity of the rhenium carbonyl system for increased C₅ +yield. In this particular case, this was accomplished by runningCatalyst B at a 100 psi lower pressure than used for the runs forCatalyst A and C (i.e. 200 psig.). All other parameters of the run forCatalyst B were maintained at the same values previously used for theruns for Catalysts A and C. A study of the results for Catalyst Bpresented in FIGS. 1, 2 and 3 indicates that the increase in severitylevel associated with the drop in pressure for Catalyst B was sufficientto raise the C₅ + yield for Catalyst B to a level which wassubstantially improved over that exhibited by the control catalyst.Likewise the difference between the hydrogen purities in the recyclegases for the control catalyst and for Catalyst B as plotted in FIG. 2was greatly diminished indicating that some surpression ofhydrogenolysis activity had been accomplished by means of severity levelvariation. The outstanding feature of this severity modification inconditions is presented in FIG. 3 wherein it is shown that thisrelatively major increment in severity accomplished by means of apressure variation had little effect on the striking activitycharacteristic of the present catalyst system. In other words, the datapresented in the attached Figures clearly show that the present catalystsystem can use a pressure variation to trade approximately 8 to 10degrees of the activity advantage for approximately a 3 percentimprovement in C₅ + yield. Of course it is to be emphasized that thistrade-off of activity for C₅ + yield for the present catalyst system wasaccomplished at little or no sacrifice in stability chracteristics andwhile retaining a substantial activity advantage over the conventionalcatalyst system.

In final analysis, it is clear from the data presented in FIGS. 1, 2 and3 for Catalysts A, B and C that the use of a pyrolyzed rhenium carbonylcomponent to interact with a platinum-containing catalytic compositeprovides an efficient and effective means for significantly promoting anacidic hydrocarbon conversion catalyst containing a platinum group metalwhen it is utilized in a high severity reforming operation. It islikewise clear from these results that the catalyst system of thepresent invention is a difference in kind rather than degree from theplatinum-rhenium catalyst systems of the prior art.

It is intended to cover by the following claims all changes andmodifications of the above disclosure of the present invention whichwould be self-evident to a man of ordinary skill in the hydrocarbonconversion art or in the catalyst formulation art.

I claim as my invention:
 1. A catalytic composite comprising acombination of a catalytically effective amount of a pyrolyzed rheniumcarbonyl component with a porous carrier material containing a uniformdispersion of a catalytically effective amount of a platinum groupcomponent maintained in the elemental metallic state.
 2. A catalyticcomposite as defined in claim 1 wherein the platinum group component isplatinum.
 3. A catalytic composite as defined in claim 1 wherein theplatinum group component is palladium.
 4. A catalytic composite asdefined in claim 1 wherein the platinum group component is rhodium.
 5. Acatalytic composite as defined in claim 1 wherein the platinum groupcomponent is iridium.
 6. A catalytic composite as defined in claim 1wherein the porous carrier material contains a catalytically effectiveamount of a halogen component.
 7. A catalytic composite as defined inclaim 6 wherein the halogen component is combined chloride.
 8. Acatalytic composite as defined in claim 1 wherein the porous carriermaterial is a refractory inorganic oxide.
 9. A catalytic composite asdefined in claim 8 wherein the refractory inorganic oxide is alumina.10. A catalytic composite as defined in claim 1 wherein the compositecontains the components in an amount, calculated on an elementalmetallic basis, corresponding to about 0.01 to about 2 wt. % platinumgroup metal and about 0.01 to about 5 wt. % rhenium.
 11. A catalyticcomposite as defined in claim 6 wherein the halogen component is presenttherein in an amount sufficient to result in the composite containing,on an elemental basis, about 0.1 to about 3.5 wt. % halogen.
 12. Acatalytic composite as defined in claim 1 wherein the composite isprepared by the steps of: (a) reacting a rhenium carbonyl compound witha porous carrier material containing a uniform dispersion of a platinumgroup component maintained in the elemental metallic state, andthereafter, (b) subjecting the resulting reaction product to pyrolysisconditions selected to decompose the rhenium carbonyl component.
 13. Acatalytic composite as defined in claim 12, wherein the pyrolysis stepis conducted under anhydrous conditions and in the substantial absenceof free oxygen.
 14. A catalytic composite comprising the pyrolyzedreaction product formed by reacting a catalytically effective amount ofa rhenium carbonyl compound with a porous carrier material containing auniform dispersion of a catalytically effective amount of a platinumgroup metal maintained in the elemental metallic state, and thereaftersubjecting the resulting reaction product to pyrolysis conditionsselected to decompose the rhenium carbonyl component.
 15. A catalyticcomposite as defined in claim 14 wherein the porous carrier materialcontains a catalytically effective amount of a halogen component.
 16. Acatalytic composite as defined in claim 15 wherein the halogen componentis combined chloride.